According to a first aspect of the invention, there is provided a method of removing contaminants from a contaminated gas or vapour stream, which method includes passing a contaminated gas or vapour stream through a bed of curled separating media in an upward direction; allowing a contaminant in the contaminated gas or vapour stream to collect on the separating media as the gas or vapour stream passes through the bed of separating media, thereby removing the contaminant from the gas or vapour stream and thus purifying the gas or vapour stream; allowing the contaminant that has collected on the separating media to pass from the separating media into a collection zone; removing the contaminant from the collection zone; and withdrawing a purified gas or vapour stream from the bed of separating media.
While the method of the invention can, at least in principle, be used to removal contaminants from a wide range of contaminated gas or vapour streams, it is envisaged that it will have particular application in the food industry to remove contaminants such as fats and oils from contaminated air streams emanating from cooking installations.
The thickness of the separating media bed, ie its thickness in the direction in which the gas or vapour stream passes through it, may be between 3 cm and 15 cm, ie typically between 5 cm and 12 cm.
By curled separating media′ is meant separating media comprising strips shaped to have the form of at least a partial ringlet or spiral.
In one embodiment of the invention, the curled separating media may each have a dimension or length of between 3 mm and 30 mm, eg from 15 mm to 20 mm. Typically, the curled separating media may then be in the form of metal shavings, eg aluminium or steel shavings. The thickness of the shavings may be less than 1 mm, and even less than 0.5 mm, eg about 0.1 mm, while the widths of the shavings may be between 1 mm and 1 Omm, eg about 5 mm. The radius of curvature of the shavings may be between 2 mm and 15 mm, eg about 8 mm. The length of the metal strips obtained by straightening the shavings may be between 30 mm and 100 mm, eg between 50 mm and 60 mm. The shavings may thus be of spiral or ringlet form. The separating media will then be arranged in irregular fashion in the bed.
However, in another embodiment of the invention, some or all of the curled separating media may be of elongate form, and may comprise a plurality of full spirals so that they are then each a spiral separating medium. Each spiral separating medium may then be of constant diameter along its length. The spiral separating media may be arranged in a regular fashion or pattern in the bed. Thus, the spiral separating media may extend parallel to each other in the bed, and the direction of movement or passage of the gas or vapour stream through the bed may be orthogonally to the longitudinal axes of all the spiral separating media. Thus, the bed may comprise a plurality of layers of the spiral separating media, with each layer comprising a plurality of the separating media located adjacent each other, eg in abutting relationship. Each layer of the separating media will thus rest on the separating media of the layer below it. Adjacent separating media in a layer may be of opposite hand, ie their spirals may rotate or extend in opposite directions. All the spiral separating media in a particular layer may be of the same diameter and length. In one embodiment, all the spiral separating media in all the layers may be of the same diameter and length. Smaller diameter media may then, if desired, be provided at the sides of some of the rows, to fill voids on the sides of the rows. However, in another embodiment, the separating media of alternate layers may be of the same diameter, D1, while the separating media of the intermediate layers may be of the same diameter, D2, where D1 is different to D2. Other combinations of differing diameter separating media can be used, if desired.
The gas or vapour stream may be at an elevated temperature, with the contaminant being in condensable vaporized form and/or in the form of fine droplets entrained or dispersed in the gas or vapour stream.
When the contaminated gas or vapour stream is a contaminated air stream emanating from a cooking installation, the air stream will thus be hot, and typically may be at about 170° C. The contaminants in the hot air stream will then be fat and/or oils which will be present in the hot contaminated air stream in the form of fine entrained droplets and/or in vaporized form. As the hot contaminated air stream passes through the bed of curled separating media, the droplets will impinge against the curved surfaces of the media, run down the media surfaces, and drip from the media into the collection zone. Any vaporized contaminants may condense on the separating media, run down the media surfaces and drip from the media into the collection zone.
The contaminated gas or vapour stream may thus be an off or waste gas stream emanating from a household, commercial or industrial cooker.
However, more specifically, the method may include, prior to passing hot contaminated air emanating from the cooker through the bed of curled separating media, admixing the hot contaminated air with cold air. The cold air will serve to condense any vaporized fats and oils in the contaminated air so that they will be converted into entrained liquid droplet form before encountering the bed of separating media.
The process may also include passing the purified gas or vapour stream through a scrubber for removing an undesired substance such as ammonia therefrom, and/or passing it through a biological filter for removal of a substance such as sulphur therefrom, before discharging the treated gas or vapour stream to atmosphere.
More specifically, the contaminated gas or vapour stream may pass linearly, in the upward direction, through the bed of separating media. The linear velocity of the gas or vapour stream through the bed may be up to 6 m/s, and is preferably about 3.2 m/s.
According to a second aspect of the invention there is provided apparatus for removing contaminants from a contaminated gas or vapour stream, which apparatus includes a gas/vapour chamber; a gas/vapour inlet leading into the chamber; a gas/vapour outlet leading from the chamber; separating means located in proximity to the gas/vapour inlet, the separating means comprising a bed of curled separating media, with the separating means adapted such that a contaminated gas or vapour stream that enters the chamber passes through the bed of curled separating media in an upward direction, with the curled separating media acting to separate contaminants from the gas or vapour as the gas or vapour stream passes through the bed; and collecting means for collecting contaminant that has collected on the separating media.
The chamber may be defined by a plurality of walls. Thus, for example, a front wall, a rear wall spaced from the front wall, top and bottom walls, and a pair of spaced side walls located between the front, bottom, rear and top walls, may be provided. The gas/vapour inlet may be provided in the front wall, while the gas/vapour outlet will then be provided in one of the other walls. The front wall may slope downwardly inwardly from the top wall to the bottom wall, so that it is thus inclined at an angle to the vertical. The front wall may be planar.
The separating means may comprise a holder which holds the separating media bed. The holder may comprise a base, a roof spaced from the base, and a pair of spaced sides between the roof and the base. The base, roof and sides may be in the form of plates. At the front of the holder, the base, roof and side plates may define a gas/vapour inlet opening, while a gas/vapour outlet opening may be defined by the base, roof and side plates at the rear of the holder. The inlet and outlet openings may be covered by apertured coverings, eg pieces of mesh or screens, holding the separating media bed in position.
The curled separating media and the bed of curled separating media may be as hereinbefore described.
The holder may be releasably mounted inside the chamber. More particularly, it may be releasably mounted in the gas/vapour inlet of the chamber, so that its plates extend transversely, preferably orthogonally, with respect to the chamber front wall. It will thus be located at an angle to the horizontal so that a contaminated gas/vapour stream that enters the gas/vapour inlet opening of the holder passes upwardly, and preferably linearly, through the separating means before exiting through the gas/vapour outlet opening of the holder.
The apparatus may thus include mounting means mounting the holder releasably to a wall of the chamber. The holder may be provided, in proximity to its gas/vapour inlet opening, with an outwardly protruding flange which engages the wall of the chamber around the gas/vapour inlet in the chamber wall. The mounting means may then include retaining means for retaining the holder flanges in position against the chamber wall. For example, the retaining means may comprise a channel member on the chamber wall for receiving a bottom flange of the holder, and a spring biased clip adapted to engage an upper flange of the holder releasably.
The collecting means may comprise a trough located below the gas/vapour inlet of holder of the separating means. The trough may comprise a base plate, a pair of spaced side plates and a front plate closing off the front edges of the base and side plates. The base plate of the trough may thus be fast with, eg formed integrally with, the base plate of the holder. Similarly, the side plates may each be fast with, eg formed integrally with, a side plate of the holder. Thus, the holder and trough may be in the form of a holder/trough combination.
The chamber may form part of an air collection hood located above cooking apparatus, such as a stove, griller, cooker, or the like.
According to a third aspect of the invention, there is provided a holder/trough combination for an apparatus for removing contaminants from a contaminated gas or vapour stream, the combination including a holder for holding a separating media bed, the holder comprising a base plate, a roof plate spaced from the base plate, and a pair of spaced side plates between the roof and base plates, with the base plate, the roof plate and the side plate defining, at the front of the holder, a gas/vapour inlet opening, while a gas/vapour outlet opening is defined by the base plate, the roof plate and the side plates at the rear of the holder; and a trough located below the gas/vapour inlet opening of the holder.
The trough may comprise a base plate, a pair of spaced side plates and a front plate closing off the front edges of the base and side plates, with the base plate of the trough being fast with the base plate of the holder, as hereinbefore described.
A bed of curled separating media, as hereinbefore described, may be provided inside the holder.
According to a fourth aspect of the invention, there is provided a cooking installation which includes cooking apparatus on which foodstuffs can be cooked; apparatus for removing contaminants from a contaminated air stream, according to the second aspect of the invention, above the cooking apparatus; an air extraction conduit leading from the air collection hood of the apparatus such that an inlet to the conduit is in communication with the gas/vapour outlet in one of the walls of the air collection hood; and air extraction means in or associated with the extraction conduit.
The cooking apparatus may, in particular, be adapted such that foodstuffs can be grilled thereon, eg by means of a gas flame. For example, it may be a gas cooker.
The conduit may be in the form of a duct. The extraction means may be an extraction fan mounted in the duct.
Apart from hot fat and oil laden air entering the separating apparatus, in use, cold air will also be drawn in from underneath the hood, with the cold air serving to condense the fats and oils from a gaseous form at a high temperature, typically about 170° C. immediately above the cooking apparatus, to a liquid form at a lower temperature, typically between ambient temperature and 100° C., eg 20° C. to 70° C., at which temperature all oils and fats are in liquid form and at which temperature efficient separation thereof in the bed of curled separating media can be effected.